1. Field of the Invention
The present invention relates to a magnetooptical information recording and/or reproducing method capable of performing overwriting by magnetic field modulation and utilizing a floating slider supporting a magnetic head, and an apparatus therefor.
2. Related Background Art
In a magnetooptical information recording/reproducing apparatus, or in a magnetooptical disk apparatus, a magnetooptical disk constituting the information recording medium is irradiated with a laser beam spot for heating the irradiated area under the application of a magnetic field, and the recording or erasure of information is conducted by the scanning movement of said light spot.
Among such recording methods, there is known a light modulation recording method in which the laser beam is on-off modulated according to the recording information while the intensity and polarity of the applied magnetic field are maintained constant (for example, using a ISO standard magnetooptical disk). This method enables so-called pit position recording, in which the reproduction signal is obtained from the center position of the recorded pit.
Now reference is made to FIG. 1 for explaining the light modulation recording method. There are illustrated a magnetooptical disk 1001; an information recording film 1002 and a protective film 1003 thereof; an objective lens 1004 of an optical head, for condensing the laser beam from an unrepresented light source onto the recording film 1002 of the disk; a light 1005 emerging from said objective lens 1004 and forming a light spot on the recording film 1002; and a bias magnet 1006 for applying a magnetic field of a predetermined intensity to the magnetooptical disk.
During information recording, at first a magnetic field of predetermined polarity and intensity is applied by the bias magnet 1006 to the magnetooptical disk 1001, and the laser beam 1005 of a recording power simultaneously irradiates the recording film 1002, thereby erasing the information recorded therein. Then the information is recorded by inducing inversion of magnetization in the recording film 1002, by applying a magnetic field of opposite polarity and a predetermined intensity to the magnetooptical disk and modulating the laser beam with the recording information.
In recent years, however, there is desired so-called pit edge recording, in which the reproduction signal is obtained from both ends of a recorded pit, for the purpose of increasing the recording capacity. For such pit edge recording there is generally employed a magnetic field modulation recording method, in which the direction (polarity) of the magnetic field is suitably inverted in a short time by means of a small magnetic head, while the laser beam irradiation is conducted with a constant intensity.
Now reference is made to FIG. 2 for explaining the magnetic field modulation recording method. There are illustrated a magnetooptical disk 1011; an information recording film 1012 and a protective film 1013 thereof; a floating slider 1015 supporting an unrepresented small magnetic head; a support member 1016 supporting said floating slider; an object lens 1004 of an optical head, for condensing the laser beam from an unrepresented light source onto the recording film 1012, and a light 1005 emerging from the objective lens 1004 and forming a light spot on the recording film 1012.
During information recording, a laser beam of a constant intensity of a recording power is concentrated on the recording film 1012 of the magnetooptical disk. At the same time the recording film 1012 is given a magnetic field, modulated by the recording information, generated by the magnetic head in the floating slider 1015. This method enables overwriting, in which the recording is achieved simultaneously with the erasure of the information already recorded in the recording film 1012. It also increases the recording capacity in comparison with the above-explained light modulation recording method, and improves the transfer rate.
The above-mentioned floating slider floats from the disk, utilizing the dynamic pressure of air, generated by the rotation of the disk.
Since the floating slider 1015 floats by a distance of 5 to 10 .mu.m from the protective film 1013 of the magnetooptical disk, said protective film is required to have an elevated smoothness (surface precision), a low friction coefficient and a high abrasion resistance. In the magnetooptical disk for the aforementioned light modulation recording method, the protective film 1003 does not have such strict requirements and is generally inferior, in the smoothness, friction coefficient and abrasion resistance, to the protective film 1013 of the magnetooptical disk for the magnetic field modulation recording method. For this reason, if information recording and/or reproduction is conducted with the former magnetooptical disk in combination with a floating slider, said slider does not slide satisfactorily with respect to the protective film and both the magnetooptical disk and the floating slider may be damaged.
Consequently, the magnetooptical disk for light modulation recording and that for magnetic field modulation have respectively been recorded or reproduced in exclusive apparatus. However, such a lack of compatibility between the recording media of two recording methods is undesirable. Also, the floating slider and the magnetooptical disk have often been damaged by mistaken loading of the disk for light modulation recording in the apparatus for magnetic field modulation recording method.